Hum-free single coil P-90... how can this be?

[Steve A.]

I bought a blue MIK Epiphone Casino in the mid-90's. I haven't played it for years so I thought I would take it for a spin. It came with two P-90's in metal covers which I upgraded with Gibsons which I mounted with the metal covers. I wanted the middle position to be humcancelling so I flipped the magnets and reversed the coil wires on one of them. I have a power strip with FX transformers mounted on the leg of my amp bench so if I am too close it will cause some guitars to hum (a bit or a lot.)

Surprise, surprise! There was hardly any hum at all from the neck pickup, but plenty of hum from bridge pickup and the middle position. The only difference between the two pickups and their wiring was the flipped magnets and the reversed coil wires on one of them (I don't remember which after all of these years.) I'm thinking that the low-hum pickup has the ground lead connected to the outside of the coil and might be acting as shielding to some extent. One other observation: 4 of the 6 pole pieces of the "hummy" pickup are grounded, only one of them is ground with the low-hum pickup. (I may have wrapped teflon tape around the pole pieces- I dunno.)

The guitar is long overdue for a restringing so I will be able to investigate a little more but not right now. Any ideas? BTW I know I was careful in flipping the magnets- I would mark them with a Sharpie to make sure that I flipped them in the right direction- but I still might have screwed up.

Thanks!

Steve Ahola

P.S. This Epi Casino is the notorious "Blue Guitar." The big "E" on the pickguard reminded me of Otis Rush's 1st album: "Mourning in the Morning." I'll have to take a picture since the blue is very distinctive- kinda like the metallic blue in this picture:

[jonson]

Pelham Blue..

[David Schwab]

I'd bet that the start on the hum free pickup is to ground. Take the one that hums, flip the bobbin over, and then rewire it the way it was originally. Now the starts will be the same, and the winding direction on the noisy coil will be reversed. Of course you will have to remove all the poles, etc. Shouldn't be too hard though.

And yeah, Pelham Blue.

[Steve A.]

I'd bet that the start on the hum free pickup is to ground. Take the one that hums, flip the bobbin over, and then rewire it the way it was originally. Now the starts will be the same, and the winding direction on the noisy coil will be reversed. Of course you will have to remove all the poles, etc. Shouldn't be too hard though.

I was just now thinking of flipping the bobbin around instead of reversing the leads. At this point I don't know if the low-hum pickup is the one I screwed around with or not.

So will metal covers reduce the hum on single coils? I hadn't noticed that when splitting humbucker coils. I did not do a comprehensive noise test so the low-hum pickup might not work so well with others sources of noise. I believe that the Gibson P-94 has a metal cover- is that less noisy than a P-90 with a plastic cover?

Thanks!

Steve Ahola

[David Schwab]

I was just now thinking of flipping the bobbin around instead of reversing the leads. At this point I don't know if the low-hum pickup is the one I screwed around with or not.

Well if it's quiet, and the other one isn't, then you want to screw with the noisy one! You should be able to tell by looking at the wires, no?

So will metal covers reduce the hum on single coils? I hadn't noticed that when splitting humbucker coils. I did not do a comprehensive noise test so the low-hum pickup might not work so well with others sources of noise. I believe that the Gibson P-94 has a metal cover- is that less noisy than a P-90 with a plastic cover?

A grounded metal cover will help with electrical field noise. Wont do much for 60 Hz hum though.

[Steve Conner]

If I found a hum-free P90 I'd suspect it of being broken. Is it signal-free too?

[David Schwab]

I used to have an ES-330TD with the metal covered P-90s. That was a pretty quiet guitar, even when used with a Big Muff. I don't remember much hum at all.

[Steve A.]

Well if it's quiet, and the other one isn't, then you want to screw with the noisy one!

I just removed the strings and pulled out the pickups and it was the one with the reversed leads that was noisy. I'll switch that around later today. (I'm glad I got my new W60P. I loved my old one- it was great for everything but the finer pcb type work.)

So with the start of the coil grounded you have a ground on both the inside and the outside of the coil which would make it quieter (not to mention being completely enclosed in metal)? I made a few more tests- when rotating the guitar to the quietest position I could hear no difference in noise between the two pickups.

Thanks!

Steve Ahola

[sprocket]

I bought a blue MIK Epiphone Casino in the mid-90's. I haven't played it for years so I thought I would take it for a spin. It came with two P-90's in metal covers which I upgraded with Gibsons which I mounted with the metal covers. I wanted the middle position to be humcancelling so I flipped the magnets and reversed the coil wires on one of them. I have a power strip with FX transformers mounted on the leg of my amp bench so if I am too close it will cause some guitars to hum (a bit or a lot.)

Surprise, surprise! There was hardly any hum at all from the neck pickup, but plenty of hum from bridge pickup and the middle position. The only difference between the two pickups and their wiring was the flipped magnets and the reversed coil wires on one of them (I don't remember which after all of these years.) I'm thinking that the low-hum pickup has the ground lead connected to the outside of the coil and might be acting as shielding to some extent. One other observation: 4 of the 6 pole pieces of the "hummy" pickup are grounded, only one of them is ground with the low-hum pickup. (I may have wrapped teflon tape around the pole pieces- I dunno.)

The guitar is long overdue for a restringing so I will be able to investigate a little more but not right now. Any ideas? BTW I know I was careful in flipping the magnets- I would mark them with a Sharpie to make sure that I flipped them in the right direction- but I still might have screwed up.

Thanks!

Steve Ahola

P.S. This Epi Casino is the notorious "Blue Guitar." The big "E" on the pickguard reminded me of Otis Rush's 1st album: "Mourning in the Morning." I'll have to take a picture since the blue is very distinctive- kinda like the metallic blue in this picture:

[ATTACH=CONFIG]18149[/ATTACH]

Love these old muscle cars , nice Firebird there .

[David Schwab]

I just removed the strings and pulled out the pickups and it was the one with the reversed leads that was noisy. I'll switch that around later today. (I'm glad I got my new W60P. I loved my old one- it was great for everything but the finer pcb type work.)

So with the start of the coil grounded you have a ground on both the inside and the outside of the coil which would make it quieter (not to mention being completely enclosed in metal)? I made a few more tests- when rotating the guitar to the quietest position I could hear no difference in noise between the two pickups.

Thanks!

Steve Ahola

I've been winding some Fender style pickups lately. What I notice is that if the start of the coil is hot, the magnets or metal poles will induce noise in the pickup. If you keep that end grounded it won't. Makes sense when you think about it.

If the metal cover is grounded, then that's a shield.

I fully shield all my bass humbuckers, and the poles are grounded. When you switch them into single coil mode they are extremely quiet.

[Steve A.]

I've been winding some Fender style pickups lately. What I notice is that if the start of the coil is hot, the magnets or metal poles will induce noise in the pickup.

I have grounded the poles of many of the Fender style pickups I have bought. Would that make a difference? If I detect any leakage between the pole and the coil I skip that pole. (I used to use a conductive silver paint pen before they became too expen$ive.)

As a disciple of Dan Torres I used to pot and shield all of the pickups I'd buy. Which was a shame when I did it to some of the boutique pickups I bought from him. I learned that there is a certain airiness to a vintage-style pickup that can be lost when you pot them and wrap the coils with copper foil tape. Of course that airiness comes with a price- it makes the pickup very susceptible to electromagnet and RF noise, as well as microphonics. So I generally leave the new pickups I buy alone until I notice a problem with them (like an older BB3 which was very microphonic in a semi-hollow PRS SE Custom.)

You are a pickup maker and you have good reason to do what you do (shielding and potting)- customers rarely call up to complain that a pickup isn't noisy enough. And nowadays there are a lot more guitarists into high gain than vintage sounds.

Thanks!

Steve Ahola

P.S. I'll have to look at some of my Fender style pickups to see whether the start was grounded or not (that would usually be the wire coming out of the coil closest to the center point- right?)

[David Schwab]

I learned that there is a certain airiness to a vintage-style pickup that can be lost when you pot them and wrap the coils with copper foil tape.

I don't think potting changes the tone, after all Fender potted their pickups. But if you wrap foil around it in a closed loop you will flatten the resonant peak a bit and dull the high end. The trick is to not close the loop. Keep the two ends insulated from each other.

But the shielding mostly helps with the high pitched buzz you get, and not hum.

[Marko Ursin]

Steve A: do you happen to have Finnish roots in your family somewhere? Ahola is pretty common surname around here.
Marko

[Steve A.]

I don't think potting changes the tone, after all Fender potted their pickups.

You're right- I think Fender almost had to pot their pickups just so they would not fall apart and come unraveled. I seem to remember that the pickups on my DuoSonic or Mustang might not have been potted but I'd have to dig them up. I think that potting might make more of a difference with humbuckers, like solidifying a coil that might otherwise be microphonic. I got a 4-wire BurstBucker 3 a few months ago and found that they are potted (the 2 wire ones aren't- at least they weren't in the past.) I remember some people complaining that Lindy Fralin overpotted his humbuckers giving them a more compressed sound. I wonder if HB coils might be more unbalanced than a DCR reading would indicate.

But if you wrap foil around it in a closed loop you will flatten the resonant peak a bit and dull the high end. The trick is to not close the loop. Keep the two ends insulated from each other.

Thanks for the tip! A closed loop might also act as an antenna (which is why there are usually only 3 ground leads between the 4 pots in a LP.)

Steve Ahola

P.S. So what is the potting history of Gibson?

P.P.S. 7 of my 8 great grandparents were Finnish, the other one was Swedish. I was told that there was an Ahola who was powerful in Sweden in the 16th or 17th century and that many Finns took on the name perhaps to win favor with the Swedes. I just read that the first corporation was Swedish- a copper mining company in the 12th century- and that gave Sweden a lot of power. Just like Spain became very powerful in the 16th century with all of the silver they took from Mexico and South America.

[David Schwab]

You're right- I think Fender almost had to pot their pickups just so they would not fall apart and come unraveled. I seem to remember that the pickups on my DuoSonic or Mustang might not have been potted but I'd have to dig them up. I think that potting might make more of a difference with humbuckers, like solidifying a coil that might otherwise be microphonic. I got a 4-wire BurstBucker 3 a few months ago and found that they are potted (the 2 wire ones aren't- at least they weren't in the past.) I remember some people complaining that Lindy Fralin overpotted his humbuckers giving them a more compressed sound. I wonder if HB coils might be more unbalanced than a DCR reading would indicate.

I have a '72 Mustang, and they are potted.

Thanks for the tip! A closed loop might also act as an antenna (which is why there are usually only 3 ground leads between the 4 pots in a LP.)

How many ground leads do you need? They just wanted to connect them together. Then they often sit on an aluminum ground plate, so they are all connected.

The reason the loop around the coil changes the tone is because the loop is generating current, which then generates a magnetic field. That won't happen with the pots.

Bill lawrence had a patent on a secondary loop around a pickup to control the tonality.

P.S. So what is the potting history of Gibson?

I don't know, but I guess when Les Pauls got popular again after the whole Super Strat craze, they were being used at high gain, and were probably squealing. Then again, Bill Lawrence designed a lot of pickups for Gibson that were epoxy potted.